Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 6,500	$ 2,000	$ 19,400	$ 5,200
Goodwill [Line Items]
Goodwill	1,409,822	$ 236,335	1,409,822	$ 236,335	$ 1,386,853	$ 191,371
Non-Strategic
Goodwill [Line Items]
Gross goodwill	200,000		200,000		200,000
Accumulated impairments	114,100		114,100		114,100
Accumulated divestiture related write-offs	85,900		85,900		85,900
Goodwill	$ 0		$ 0		$ 0